Role of notch signalling in mammary gland
Başlık çevirisi mevcut değil.
- Tez No: 400076
- Danışmanlar: PROF. CATHRİN BRİSKEN
- Tez Türü: Doktora
- Konular: Biyoloji, Biology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2009
- Dil: İngilizce
- Üniversite: Université de Lausanne
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Biyoloji Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 83
Özet
Mammary gland is composed of two main epithelial cell types, myoepithelialand luminal. The mechanisms involved in determination and maintenanceof them remain poorly understood. Notch signaling is known to regulate cellfate determination in other tissues like skin and nervous system. It was alsoshown that it can act as tumor suppressor or oncogene depending on the tis-sue type. The mouse models overexpressing active Notch receptors indicatedthat Notch signaling is oncogenic in the mammary gland. This observationwas followed by some descriptive and functional studies in human breastcancer and it was reported that Notch signaling activity or expression of itscomponents are increased in some of the breast tumor samples compared tonormal tissue. However, the physiological role of the Notch signaling andits downstream mechanisms in mammary gland is poorly dened. p63, amember of p53 family, has been implicated in the cell fate determinationof keratinocytes. Knockout mouse models revealed that p63 is required forthe formation of the mammary anlagen in embryo and its N isoform isexpressed exclusively in the myoepithelial layer of the adult breast.In order to understand its function in normal breast epithelial cells, I ac-tivated Notch signaling by expression of Notch1 intracellular domain (NICD)in normal primary human breast epithelial cells (HBECs). In this context,NICD reduced growth of HBECs and led to downmodulation of extracellularmatrix-receptor interaction network (ECM) components as well as Np63.Expression of Np63 together with NICD partially rescued Notch inducedgrowth reduction, which was correlated with an increase in ECM compo-nents. Moreover, silencing Np63 in myoepithelial HBECs reduced growthsimilar to Notch activation and it led to downregulation of myoepithelial andupregulation of luminal markers. Complementing this observation, forced ex-pression of Np63 in luminal HBECs induced myoepithelial phenotype anddecreased luminal markers.In vivo, by the analysis of a Notch reporter mouse strain, I showed thatNotch is activated during puberty specically at the sites of ductal morpho-genesis, terminal end buds. FACS analysis revealed that it can be detected intwo dierent populations based on CD24 expression (low (lo) or high (high)):at lower levels in CD24lo, which includes stem/progenitor and myoepithelialcells and higher levels in CD24hi, which contains luminal cells. In parallelwith in vitro results, the CD24lo mouse mammary epithelial cells display-ing Notch activity have lower levels of p63 expression. Furthermore, dele-tion of RBPj, the main mediator of Notch signaling, or the overexpressionof Np63 inhibited luminal cell lineage in vivo. Another important pointrevealed by Notch reporter mouse strain is the simultaneous activation ofNotch with estrogen signaling during pubertal development. The expressionof FOXA1, the mediator of estrogen receptor (ER) transcriptional activity,is correlated with Notch activation in vivo that it is lower in CD24lo than inCD24hi cells. Moreover, FOXA1 is regulated by NICD in vitro supportingthe presence of a link between Notch and ER signaling.Taken together, I report that Notch signaling is involved in luminal cellfate determination and its eects are partially mediated through inhibitionof Np63. Besides, Np63 is required for the maintenance and sucientfor the induction of myoepithelial phenotype in HBECs in vitro and is notcompatible with luminal lineage in vivo.Based on these results, I propose a model for epithelial cell hierarchy inmammary gland, whereby there are two different types of luminal progeni-tors, early and late, displaying different levels of Notch activity. Notch sig-naling contributes to the determination of luminal cell lineage in these twoprogenitor steps: In \Early Luminal Progenitor“ stage, it inhibits myoep-ithelial fate by decreasing p63 expression, and in \Late Luminal Progenitor”stage, Notch signaling is involved in induction of luminal lineage by acting onER-FOXA1 axis. It has to be investigated further whether Notch signalingmight behave as an oncogene or tumor suppressor depending on which celltype in the epithelial hierarchy it is modulated and which one is more likelyto occur in different human breast cancer types.
Özet (Çeviri)
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